Liquid crystal display device and method of manufacturing the same

ABSTRACT

An LCD device and a method of manufacturing the same are disclosed, which prevents a liquid crystal from being filled imperfectly or excessively in an active region, thereby obtaining a uniform cell gap and improving picture quality characteristics. The LCD device includes a lower substrate and an upper substrate, a UV sealant between the lower and upper substrates, the UV sealant having a portion for controlling a liquid crystal flow at four corner regions, and a liquid crystal layer between the lower and upper substrates.

This application claims the benefit of Korean Patent Application No.P2002-15079 filed on Mar. 20, 2002, which is hereby incorporated byreference for all purposes as if fully set forth herein.

This application incorporates by reference two co-pending applications,Ser. No. ______, filed on Jun. 28, 2002, entitled “SYSTEM AND METHOD FORMANUFACTURING LIQUID CRYSTAL DISPLAY DEVICES” (Attorney Docket Number8733.666.00) and Ser. No. ______, filed on Jun. 28, 2002, entitled“SYSTEM FOR FABRICATING LIQUID CRYSTAL DISPLAY AND METHOD OF FABRICATINGLIQUID CRYSTAL DISPLAY USING THE SAME” (8733.684.00), as if fully setforth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display (LCD) device,and more particularly, to a sealant pattern of an LCD device.

2. Discussion of the Related Art

Generally, ultra thin flat panel displays having a display screen with athickness of several centimeters or less, and in particular, flat panelLCD devices, are widely used in monitors for notebook computers,spacecraft, and aircraft in view of the aspects that such LCD deviceshave low power consumption and are easy to carry.

Such an LCD device, as shown in FIG. 1, includes a lower substrate 1, anupper substrate 3, and a liquid crystal layer 5. A thin film transistor(TFT) (not shown) and a pixel electrode (not shown) are formed on thelower substrate 1. The upper substrate 3 is formed to oppose the lowersubstrate 1. A light-shielding layer (not shown), a color filter layer(not shown), and a common electrode (not shown) are formed on the uppersubstrate 3. The liquid crystal layer 5 is formed between the lower andupper substrates 1 and 3.

A sealant 7 is formed between the lower and upper substrates 1 and 3 toprevent the liquid crystal layer 5 from leaking out.

In the aforementioned LCD device, to form the liquid crystal layer 5between lower and upper substrates 1 and 3, a vacuum injection methodbased on capillary phenomenon and pressure difference has beenconventionally used. However, such a vacuum injection method has aproblem in that it takes long time to inject the liquid crystal over alarge panel area, thereby reducing the productivity.

To solve such a problem, a method of applying liquid crystal to one ofthe substrates has been supposed.

A method of manufacturing an LCD device based on a liquid crystaldropping method will now be described with reference to FIGS. 2A to 2D.

As shown in FIG. 2A, a lower substrate 1 and an upper substrate 3 areprepared. A plurality of gate and data lines (not shown) are formed onthe lower substrate 1. The gate lines cross the data lines to define apixel region. A thin film transistor (not shown) is formed at eachcrossing point between the gate and data lines. A pixel electrode (notshown) connected with the thin film transistor is formed in the pixelregion.

A light-shielding layer (not shown) is formed on the upper substrate 3to prevent light from leaking out from the gate and data lines and thethin film transistor. Color filter layers of red(R), green(G), andblue(B) are formed on the light-shielding layer, and a common electrode(not shown) is formed on the color filter layers. An alignment film (notshown) is formed on at least one of the lower substrate 1 and the uppersubstrate 3 to initially align a liquid crystal.

As shown in FIG. 2B, a sealant 7 is formed on the lower substrate 1 anda liquid crystal 5 is dropped thereon, so that a liquid crystal layer isformed. A spacer (not shown) is spread or sprayed onto the uppersubstrate 3 to maintain a cell gap.

In the method of manufacturing the LCD device based on the liquidcrystal application method, a liquid crystal layer is formed on bondedsubstrates. Therefore, if a thermo-hardening sealant is used as thesealant 7, the sealant 7 heats and expands and flows out of thesubstrate when it is heated. For this reason, a problem arises in thatthe liquid crystal 5 is contaminated.

Therefore, in the method of manufacturing the LCD based on the liquidcrystal application method, a UV sealant is used as the sealant 7.

As shown in FIG. 2C, the lower substrate 1 is attached to the uppersubstrate 3.

As shown in FIG. 2D, UV is irradiated through a UV irradiating device 9so that the sealant 7 is hardened, thereby bonding the lower substrate 1to the upper substrate 3.

Thereafter, although not shown, a cell cutting process and a final testprocess are performed.

The aforementioned liquid crystal dropping method has an advantage inthat it takes a short time to form the liquid crystal layer as comparedwith the vacuum injection method because the liquid crystal 5 isdirectly applied onto the lower substrate 1 before the substrates 1 and3 are bonded to each other. However, the liquid crystal applicationmethod has the following problems.

First, although an amount of the liquid crystal dropped onto thesubstrate is generally determined considering some factors such as thesize of the substrate and a cell gap between both substrates, it isdifficult to exactly determine the amount of the liquid crystal appliedon the substrate.

Accordingly, if the liquid crystal is applied in an amount less than therequired amount, regions of the substrate where the liquid crystal isfilled imperfectly, particularly, occur at four corners located farthestfrom the center of the substrate. If the liquid crystal is droppedexcessively, a partial region where the liquid crystal is filledexcessively occurs.

This deteriorates uniformity of the cell gap and picturecharacteristics.

Even if the liquid crystal is applied appropriately, it takes a certaintime to spread the liquid crystal from the center part of the substrateto the corners. Accordingly, if the imperfectly filled region occurs asthe liquid crystal is not spread to the corner regions before a finaltest process, the final test process cannot be carried out.

Finally, if the substrate is heated during the process of manufacturingan LCD device, the liquid crystal expands. In this case, a partialregion where the liquid crystal is filled excessively also occurs,thereby reducing uniformity of a cell gap.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to an LCD device and amethod of manufacturing the same that substantially obviates one or moreproblems due to limitations and disadvantages of the related art.

An advantage of the present invention is to provide an LCD device and amethod of manufacturing the same that prevents a liquid crystal frombeing filled imperfectly or excessively in an active region, therebyobtaining a uniform cell gap and improving picture qualitycharacteristics.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. These andother advantages of the invention will be realized and attained by thestructure particularly pointed out in the written description and claimshereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, a liquidcrystal display device includes a lower substrate and an uppersubstrate; a sealant between the lower and upper substrates, the sealanthaving a portion for controlling a liquid crystal flow at at least twocorner regions; and a liquid crystal layer between the lower and uppersubstrates.

In another aspect of the present invention, a liquid crystal displaydevice includes an upper substrate and a lower substrate attached to oneanother by a sealant, the sealant and the upper and lower substratesforming an enclosed volume; and liquid crystal in the enclosed volumebetween the upper and lower substrates, wherein a portion of the sealantforms at least one reservoir outside an active area of the liquidcrystal display device.

In another aspect of the present invention, a method of manufacturing aliquid crystal display device includes preparing a lower substrate andan upper substrate; forming a sealant having a portion for controlling aliquid crystal flow in at least two corner regions on one of the lowerand upper substrates; applying the liquid crystal on one of the lowerand upper substrates; attaching the substrates to each other; and curingthe sealant.

In an embodiment of the present invention, an amount of the liquidcrystal that is more than sufficient to fill a cell gap between the twosubstrates is applied to one of the substrates, so as to prevent theliquid crystal from being imperfectly filled in the cell gap between thesubstrates. Also, the UV sealant is formed on one of the two sustratesto have a part for controlling a liquid crystal flow at corner regionsso that a partial region where the liquid crystal is formed excessivelydoes not occur.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWING

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

In the drawings:

FIG. 1 is a sectional view of a general LCD device;

FIGS. 2A to 2D are perspective views illustrating a method ofmanufacturing an LCD device;

FIG. 3A is a plan view of an LCD device according to the firstembodiment of the present invention;

FIG. 3B is a sectional view taken along line I-I of FIG. 3A;

FIGS. 4A to 4D are perspective views illustrating a method ofmanufacturing an LCD device according to the second embodiment of thepresent invention; and

FIG. 4E is a perspective view illustrating a process of irradiating UVin the method of manufacturing an LCD device according to the presentinvention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Reference will now be made in detail to embodiments of the presentinvention, examples of which is illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

FIG. 3A is a plan view of an LCD device according to the firstembodiment of the present invention, and FIG. 3B is a sectional viewtaken along line I-I of FIG. 3A.

As shown in FIGS. 3A and 3B, an LCD device according to the firstembodiment of the present invention includes a lower substrate 10, anupper substrate 30, a sealant 70 that is at least partially curable byultraviolet (UV) light formed between the lower and upper substrates 10and 30, and a liquid crystal layer 50 formed within a volume formed bythe UV sealant 70 between the lower and upper substrates 10 and 30.

The UV sealant 70 is patterned to form a part 75 for controlling aliquid crystal flow at four corner regions. The part 75 is formed toreceive excess liquid crystal from an active region of the LCD device,such as a cavity, reservoir or well. Therefore, if the liquid crystal isapplied excessively, i.e., overfilled, the excess liquid crystal entersinto the part 75 away from an active region.

Also, even if the liquid crystal expands during a heating process, theexcess liquid crystal enters into the part 75 so that overfilling of theliquid crystal in the active region does not occur. If the expandedliquid crystal shrinks, the liquid crystal filled in the part 75 movesto the active region.

The size of the part 75 can appropriately be adjusted and may havevarious shapes such as a round, triangular, rectangular, polygonal, orany other shape as would be appreciated by one of skill in the art.

Although not shown, a thin film transistor and a pixel electrode areformed on the lower substrate 10. The thin film transistor includes agate electrode, a gate insulating layer, a semiconductor layer, an ohmiccontact layer, and source/drain electrodes.

Although not shown, a light-shielding layer, a color filter layer, and acommon electrode are formed on the upper substrate 30. Thelight-shielding layer shields light leakage from a region other than thepixel electrode. Additionally, an overcoat layer (not shown) may beformed on the color filter layer. In an In-Plane Switching (IPS) modeLCD device, the common electrode is formed on the lower substrate 10.

The part 75 formed by a pattern of the UV sealant 70 corresponds to aregion where the light-shielding layer is formed. Therefore, picturequality characteristics are not deteriorated even if the liquid crystal50 is filled imperfectly in the part 75.

Spacers may be formed between the substrates 10 and 30 to maintain acell gap. Ball spacers or column spacers may be used as the spacers. Theball spacers may be formed in such a manner that they are mixed with asolution having an appropriate concentration and then spread at a highpressure onto the substrate from a spray nozzle. The column spacers maybe formed on portions of the substrate corresponding to gate lines ordata lines. Preferably, the column spacers may be formed of aphotosensitive organic resin.

FIGS. 4A to 4D are perspective views illustrating a method ofmanufacturing an LCD device according to the second embodiment of thepresent invention.

Although the drawings illustrate only one unit cell, a plurality of unitcells may be formed depending upon the size of the substrate.

Referring to FIG. 4A, a lower substrate 10 and an upper substrate 30 areprepared. A plurality of gate and data lines (not shown) are formed onthe lower substrate 10. The gate lines cross the data lines to define apixel region. A thin film transistor having a gate electrode, a gateinsulating layer, a semiconductor layer, an ohmic contact layer,source/drain electrodes, and a protection layer is formed at eachcrossing point of the gate lines and the data lines. A pixel electrodeconnected with the thin film transistor is formed in the pixel region.

An alignment film (not shown) is formed on the pixel electrode toinitially align the liquid crystal. The alignment film may be formed ofpolyamide or polyimide based compound, polyvinylalcohol (PVA), andpolyamic acid by rubbing. Alternatively, the alignment film may beformed of a photosensitive material, such as polyvinvylcinnamate (PVCN),polysilioxanecinnamate (PSCN) or cellulosecinnamate (CelCN) basedcompound, by using a photo-alignment method.

A light-shielding layer (not shown) is formed on the upper substrate 30to shield light leakage from the gate lines, the data lines, and thethin film transistor regions. A color filter layer (not shown) of R, G,and B is formed on the light-shielding layer. A common electrode (notshown) is formed on the color filter layer. Additionally, an overcoatlayer (not shown) may be formed between the color filter layer and thecommon electrode. The alignment film is formed on the common electrode.

Silver (Ag) dots (not shown) are formed outside the lower substrate 10to apply a voltage to the common electrode on the upper substrate 30after the lower and upper substrates 10 and 30 are bonded to each other.Alternatively, the silver dots may be formed on the upper substrate 30.

In an in plane switching (IPS) mode LCD, the common electrode is formedon the lower substrate like the pixel electrode, and, in operation, anelectric field is horizontally induced between the common electrode andthe pixel electrode. The silver dots are not formed on the substrates.

A sealant 70 that is at least partially curable by UV light is formed onthe upper substrate 30 to have a part 75 for controlling a liquidcrystal flow at four corner regions.

The part 75 may have various shapes such as a round, triangular,rectangular, polygonal shape or any other shape as would be appreciatedby one of skill in the art with a size may appropriately adjustedaccording factors such as the level of liquid crystal applied and thesize of the substrate.

The UV sealant is formed by a screen printing method or a dispensingmethod. In the screen printing method, because a screen comes intocontact with the substrate, the alignment film formed on the substratemay be damaged. Also, if the substrate has a large area, loss of thesealant increases. In these respects, the dispensing method ispreferably used.

Monomers or oligomers each having both ends coupled to the acrylicgroup, mixed with an initiator are used as the UV sealant 70.Alternatively, monomers or oligomers each having one end coupled to theacrylic group and the other end coupled to the epoxy group, mixed withan initiator are used as the UV sealant 70.

Also, the liquid crystal 50 is applied onto the lower substrate 10 toform a liquid crystal layer. At this time, the amount of the liquidcrystal 50 is determined by considering the size of the substrate and acell gap. Preferably, the liquid crystal 50 is substantially applied inan amount greater than the minimum level sufficient to fill the cellgap.

The liquid crystal 50 may be contaminated if it comes into contact withthe UV sealant 70 before the UV sealant 70 is hardened. Accordingly, theliquid crystal 50 may preferably be applied on the central part of thelower substrate 10. In this case, the liquid crystal 50 is graduallyspread evenly after the UV sealant 70 is hardened. If the liquid crystal50 is applied excessively, the liquid crystal 50 enters into the part75. Thus, the liquid crystal 50 is uniformly distributed in the activeregion of the substrate, thereby maintaining a uniform cell gap.

Also, if the liquid crystal is applied in an amount (application amount)more than a minimum amount required to fill the cell gap in the activeregion (minimum amount), it takes a short time to spread the liquidcrystal to the corner regions so that the liquid crystal is spread tothe active region before the final test process.

Meanwhile, although FIG. 4B illustrates the process of applying theliquid crystal 50 on the lower substrate 10 and forming the UV sealant70 on the upper substrate 30, the liquid crystal 50 may be formed on theupper substrate 30 while the UV sealant 70 may be formed on the lowersubstrate 10.

Alternatively, both the liquid crystal 50 and the UV sealant 70 may beformed on one substrate. In this case, an imbalance occurs between theprocessing times of the substrate with the liquid crystal and thesealant and the substrate without the liquid crystal and the sealant.For this reason, the manufacturing process time increases. Also, whenthe liquid crystal and the sealant are formed on one substrate, thesubstrate may not be cleaned even if the sealant is contaminated beforethe substrates are attached to each other.

Accordingly, a cleaning process for cleaning the upper substrate 30 mayadditionally be provided after the UV sealant 70 is formed on the uppersubstrate 30.

Meanwhile, spacers may be formed on either of the two substrates 10 and30 to maintain a cell gap. Preferably, the spacers may be formed on theupper substrate 30.

Ball spacers or column spacers may be used as the spacers. The ballspacers may be formed in such a manner that they are mixed with asolution having an appropriate concentration and then spread at a highpressure onto the substrate from a spray nozzle. The column spacers maybe formed on portions of the substrate corresponding to the gate linesor data lines. Preferably, the column spacers may be used for the largesized substrate since the ball spacers may cause an uneven cell gap forthe large sized substrate. The column spacers may be formed of aphotosensitive organic resin.

Referring to FIG. 4C, the lower substrate 10 and the upper substrate 30are attached to each other by the following processes. First, one of thesubstrates having the liquid crystal applied thereon is placed at thelower side. The other substrate is placed at the upper side by turningby 180 degrees so that its portion having certain layers faces into thesurface of the lower substrate having certain layers. Thereafter, thesubstrate at the upper side is pressed, so that both substrates areattached to each other. Alternatively, the space between the substratesmay be maintained under the vacuum state so that both substrates areattached to each other by releasing the vacuum state.

Then, as shown in FIG. 4D, UV light is irradiated upon the attachedsubstrates through a UV irradiating device 90. Upon irradiating the UV,monomers or oligomers activated by an initiator constituting the UVsealant 70 are polymerized and hardened, thereby bonding the lowersubstrate 10 to the upper substrate 30.

If monomers or oligomers each having one end coupled to the acrylicgroup and the other end coupled to the epoxy group, mixed with aninitiator are used as the UV sealant 70, the epoxy group is notcompletely polymerized. Therefore, the sealant may have to beadditionally heated at about 120° C. for one hour after the UVirradiation, thereby hardening the sealant completely.

In the UV irradiation, if the UV light is irradiated upon the entiresurface of the attached substrates, the UV light may deterioratecharacteristics of devices such as a thin film transistor on thesubstrate and change a pre-tilt angle of an alignment film formed forthe initial alignment of the liquid crystal.

Therefore, as shown in FIG. 4E, the UV light is irradiated in a statethat an active region in the UV sealant 70 is covered with a mask 95.

Although not shown, the bonded substrates are cut into a unit cell.

In the cutting process, a cutting line is formed on a surface of thesubstrates with a pen or cutting wheel of a material that has a hardnessgreater than that of glass, e.g., diamond, and then the substrate is cutalong the cutting line by mechanical impact or breaking process. Thus, aplurality of unit cells can be obtained simultaneously.

Alternatively, the scribing process and the breaking process maysimultaneously be performed using a pen or cutting wheel of a materialthat has a hardness greater than that of glass, thereby obtaining a unitcell. In this case, space occupied by cutting equipment that cuts theglass is reduced over the space occupied by equipment required to scribeand break the glass and the overall cutting process time is also reducedover the combined scribe and break process.

As aforementioned, the LCD and the method of manufacturing the sameaccording to the present invention have the following advantages.

Since the liquid crystal the level of liquid crystal applied to thesubstrate can be greater than the amount required to cover the activearea of the LCD panel and the sealant is formed to have the part forcontrolling a liquid crystal flow, the liquid crystal is filledappropriately without any imperfections caused by an overfill in theactive area. Thus, a uniform cell gap can be maintained.

Furthermore, even if the liquid crystal expands or shrinks, for example,during the heating process, the liquid crystal exits or enters the partfor controlling a liquid crystal flow, thereby avoiding any defect in acell gap that may occur.

It will be apparent to those skilled in the art that variousmodifications and variation can be made in the present invention withoutdeparting from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. A liquid crystal display device comprising: a lower substrate and an upper substrate; a sealant between the lower and upper substrates, the sealant having a portion for controlling a liquid crystal flow at least two corner regions; and a liquid crystal layer between the lower and upper substrates.
 2. The liquid crystal display device of claim 1, wherein the sealant has the portion for controlling a liquid crystal flow at four corner regions.
 3. The liquid crystal display device of claim 1, wherein the portion has a polygonal shape.
 4. The liquid crystal display device of claim 1, wherein the portion has a round shape.
 5. The liquid crystal display device of claim 1, wherein the portion has a rectangular shape.
 6. The liquid crystal display device of claim 1, wherein the portion has a square shape.
 7. The liquid crystal display device of claim 1, wherein the portion has a triangular shape.
 8. The liquid crystal display device of claim 1, further comprising a thin film transistor and a pixel electrode on the lower substrate.
 9. The liquid crystal display device of claim 1, further comprising a light-shielding layer and a color filter layer on the upper substrate.
 10. The liquid crystal display device of claim 9, wherein a portion of the light-shielding layer corresponds to at least one portion of the sealant for controlling the liquid crystal flow.
 11. The liquid crystal display device of claim 8, further comprising a common electrode on the lower substrate.
 12. The liquid crystal display device of claim 8, further comprising a common electrode on the upper substrate.
 13. The liquid crystal display device of claim 1, further comprising spacers between the lower and upper substrates.
 14. A liquid crystal display device comprising: an upper substrate and a lower substrate attached to one another by a sealant, the sealant and the upper and lower substrates forming an enclosed volume; and liquid crystal in the enclosed volume between the upper and lower substrates; wherein a portion of the sealant forms at least one reservoir outside an active area of the liquid crystal display device.
 15. The liquid crystal display device of claim 14 having two reservoirs.
 16. The liquid crystal display device of claim 14, wherein the reservoir has a polygonal shape.
 17. The liquid crystal display device of claim 14, wherein the reservoir has a round shape.
 18. The liquid crystal display device of claim 14, wherein the reservoir has a rectangular shape.
 19. The liquid crystal display device of claim 14, wherein the reservoir has a square shape.
 20. The liquid crystal display device of claim 14, wherein the reservoir has a triangular shape.
 21. The liquid crystal display device of claim 14, further comprising a thin film transistor and a pixel electrode on the lower substrate.
 22. The liquid crystal display device of claim 14, further comprising a light-shielding layer and a color filter layer on the upper substrate.
 23. The liquid crystal display device of claim 22, wherein a portion of the light-shielding layer corresponds to at least one portion of the sealant for controlling the liquid crystal flow.
 24. The liquid crystal display device of claim 21, further comprising a common electrode on the lower substrate.
 25. The liquid crystal display device of claim 22, further comprising a common electrode on the upper substrate.
 26. The liquid crystal display device of claim 14, further comprising spacers between the lower and upper substrates. 27-43. (canceled) 